Underfloor heating goes mainstream

Space heating, Rehau, underfloor heating
Acceptance for underfloor heating — Rob Ewels.

Large buildings and underfloor heating are ideal partners for achieving comfortable and low-energy buildings with a fast payback compared with other forms of heating. Rob Ewels of Rehau takes up the story.

Over recent years, underfloor heating has successfully made the transition from a niche to a mainstream solution in the space heating sector. Because it generates radiant heat, underfloor heating is generally recognised as a more efficient and comfortable solution than either radiators or HVAC units, which rely on the principle of convection and heating air.

In a large-scale commercial project where underfloor heating is sited within a screeded floor, the large thermal mass of the floor retains that heat and releases it smoothly and consistently, concentrating it in the 2 m occupied zone.

In contrast, radiators and HVAC units demand a degree of over-specification to take into account the fact that to achieve a comfortable temperature of 20 to 21°C in the occupied zone, the temperature in the unoccupied zone near to the ceiling is likely to be closer to 28 to 30°C. In reality, in larger buildings with high ceilings, the warmth may barely be felt in the 2 m zone nearest to the floor where most of the workforce will be.

Underfloor heating also eliminates the peaks and troughs associated with convected heat when windows or doors are opened and hugely reduces the incidence of dust and allergens being circulated in moving air patterns.

The benefits have been perfectly, if rather extremely, demonstrated by in Germany where Rehau underfloor heating was installed to replace HVAC units in a 100 m long x 20 m high aircraft hangar at Munich airport. Previously, the workforce at ground level had to work in insulated layers of clothing because the occupied area of the building was always significantly cooler than the roof space and each time the hangar doors were opened there was a sudden and intense dip in temperature.

In contrast, the workforce now only requires insulated clothing when they work at height on a plane, and the dip in temperature when the doors are opened is shorter and much less severe.

Of course, it’s not just the improved comfort conditions which have given underfloor heating a rapidly growing share of the commercial heating market — it’s also the proven energy efficiency and low running costs.

We recently conducted an economic analysis for one of the UK’s major automotive manufacturers in advance of its investment in a new plant. We created a building simulation based around a 900 m² floor area with a 9.8 m ceiling height and a heat demand of 88 W/m².

Our analysis demonstrated that, whilst the capital cost of installing underfloor heating with a fully insulated floor slab was 12% higher than the cost of installing air-handling units, the annual running costs of underfloor heating using a gas-powered heat source were actually 14% lower, with the potential to recover the additional capital cost relatively quickly.

In this simulation, increasing to a double shift or even 24 h operation would actually have increased the differential in running costs still further because of the slow response times which characterise underfloor heating systems, meaning they operate most efficiently when they are not cycling on and off.

In terms of installation costs, there are obviously economies of scale available in large commercial spaces like factories, airports, warehouses and retail spaces where a great many systems are installed.

This underfloor heating system at Newbiggin Maritime Centre is served by heat pumps.

Underfloor heating is installed much more quickly and efficiently in large spaces, so laying pipe in a 100 m² hall is much quicker and more straightforward than laying in tight spaces in a domestic home. As a result, commercial installations generally generate payback even faster than domestic projects.

Of course, in addition to the comfort and the energy efficiency benefits, one of the key reasons for the continuing growth of underfloor heating systems is that they work so effectively in partnership with low-temperature renewable heat sources.

The water circulating within an underfloor heating system is typically between 35 and 45°C, compared with a traditional temperature of 70 to 80°C for radiators, meaning that the electrical demand from the heat pump is much lower and the coefficient of performance (COP) that can be achieved is much higher.

Commercial clients which are concerned with the long-term costs of a system and not just the costs of installation increasingly recognise that underfloor heating is both a low-energy and low-maintenance solution.

The technology continues to evolve in response to the demand for ever-more efficient and low-energy buildings, and manufacturers are developing a whole range of new applications from chilled ceilings to thermally activated building systems (TABS).

We are already seeing these types of systems gain much quicker acceptance in the market than underfloor heating originally did back in the 1970s and 1980s, and I can confidently predict that they will emerge as mainstream solutions in the future.

Rob Ewels is business team leader with Rehau Underfloor Heating.

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